Upshift scheduling valve for use in hydraulic transmission control system

Abstract

In a hydraulic control system for an automatic power transmission, there is provided an upshift scheduling valve by means of which the release of a frictional unit contributive to the second forward drive gear ratio is retarded in relation to the rate at which a frictional unit contributive to the third forward drive gear ratio and further with the load on the engine so that the two frictional units are permitted to be concurrently operative for an adequate period of time preventing the engine from racing during shifting from the second gear ratio to the third gear ratio in the automatic forward drive range.

What is claimed is: 
     
       1. A hydraulic control system for a transmission mechanism, comprising: a first passageway which is pressurized when a higher gear ratio is selected and which is exhausted when a lower gear ratio is selected;   an upshift scheduling valve including   a valve chamber;   a valve element slideably disposed within said valve chamber and defining within said valve chamber a compartment;   said valve chamber having a first port communicating with the first passageway and with said compartment, having a second port communicable with said compartment, and having a drain port communicable with said compartment;   said valve element having an area exposed to said compartment;   said valve element being slideable in response to pressure within said compartment to take a first position in which said second port is out of communication with said compartment, but is in communication with said drain port when said pressure in said compartment is lower than a predetermined value, and to take a second position in which said second port communicates with said first port only via said second compartment when said pressure in said second compartment is higher than said predetermined value; and   a second passageway communicating with said second port;   whereby when said first passageway is exhausted, said valve element takes said first position to allow said second passageway to communicate with said drain port to be exhausted, whereas, when said first passageway is pressurized, said second passageway is pressurized with a time lag during which said valve element moves from said first position to said second position.   
     
     
       2. A hydraulic control system for a transmission including a forward clutch including a fluid chamber, a high and reverse clutch including a fluid chamber, and a brake band having a servo unit including a brake-apply fluid chamber and a brake-release chamber, the transmission being conditioned in a lower gear ratio when the fluid chamber of the forward clutch and said brake-apply fluid chamber of said servo unit is pressurized with fluid pressure in the fluid chamber of the forward clutch and the brake-release fluid chamber of the servo unit being exhausted, and being conditioned in a higher gear ratio when the fluid chamber of the high and reverse clutch and the brake-release fluid chamber of the servo unit are pressurized with fluid pressure in the fluid chamber of the forward clutch and the brake-apply fluid chamber of the servo unit being held pressurized, the hydraulic control system comprising: a first passageway communicating with the fluid chamber of the high and reverse clutch;   an upshift scheduling valve including a valve chamber having a first port communicating with said first passageway, and a second port,   a second passageway communicating said second port with the brake-release fluid chamber of the servo unit of said band brake;   a shift valve means for pressurizing said first passageway when the higher gear ratio is established;   said up-shift scheduling valve including means responsive to said fluid pressure in said first passageway for preventing communication of said first passageway with said second passageway and allowing said second passageway to be exhausted until the fluid pressure building up in said first passageway reaches a predetermined value, and for allowing communication of said first passageway with said second passageway and preventing said second passageway from being exhausted when the fluid pressure building up in said first passageway exceeds said predetermined value;   whereby the release of the brake band is so timed with the engagement of the high and reverse clutch as to prevent racing of an engine associated with the transmission.